Manufacture of glutamic acid



Patented Dec. 5, 1950 UNITED STATES TENT OFFICE 2,533,114 MANUFACTURE OFGLUTAMI'C ACID No Drawing. ApplicationAug'ust'29, 1947,

Serial No. 771,393

The invention relates to improvements in the manufacture of glutamicacid and particularly Il(-|-) gultamic acid, sometimes called d-glutamicacid, and. is of especial value in the production of such a product bythe acid hydrolysis of proteins.

The invention will be described particularly with reference to theproduction of this material from gluten, although it will be understoodthat it is applicable to other raw materials such as protein derivedfrom soybeans which will respond to a similar treatment subject, ofcourse, to any slight differences in procedure which will be recognizedas desirable or necessary by persons skilled in the art.

Heretofore in the production of l(+) glutamic acid by either acidhydrolysis or alkaline hydrolysis, it has been necessary to produce thematerial in a more or less crude form, requiring a subsequent and rathercomplicated and expensive purification process accompanied by areduction in yield, so that the manufacturing cost of the final productis adversely affected.

The principal object of the present invention is to provide an organizedprocedure for the production of l(+) glutamic acid in the raw or initialcrystal form of such purity that no special or expensive purificationstep or procedure is required in order to obtain a product which issuitable for direct conversion into mono-sodium glutamate, which is theform in which the material is ordinarily marketed.

General method In its broadest aspects, it may be said that theinvention can be practiced according to the following general procedure:

The acid hydrolysis step.-Because of its recognized advantages from apractical operating standpoint, sulfuric acid is selected as theparticular acid which is utilized for effecting the initialhydrolyzation of the protein. This hydrolysis step is effected bysubjecting the protein to the action of sulfuric acid at a sufiicientlyhigh temperature and pressure for a sufficient length of time to effecta substantially complete hydrolysis. In this step, in the case ofgluten, it is found desirable to use the sulfuric acid in a,concentration of about 50%. With-acid at this strength, the treatment at135 C. would require about 1 to 2 hours, and if thetemperature isreduced, the length of treatment is correspondingly extended. Thegluten-acid ratio should preferably be about 1 part of gluten to 2 partsof the 50% acid.

' When the hydrolysis step is'practiced at the Claims. (Cl. 260-529)usual minimumtemperat'ure of C., the step has been completelyhydrolyzed, the hydrolysateis-allowe'd" to cool, andthere is added asulficient quantity of alkaline material, preferablyin theform of analkaline earth metal oxide or hydroxide, so'that' there will besufiicient alkaline material to react. completely with all of the S04radical to form an insolublesulfate in the form of a precipitate, whileat the same time enough alkaline material is added to raise the pH: ofthe hydrolysate to a point substantially above neutral, and specificallya pH between about l0.5'and about 11.5.

Removal of inorganic saZts.The insoluble sulfate precipitate is thenremoved by filtration or the equivalent. The filtrate will be found tocontain an additional quantity ofdeleterious metallic ions, and the nextstep in the process is for the purpose of removing these residualmetallic! ions, or at any rate that part which lateriwouldibedisadvantageous in subsequent steps 'of the processi 1 Eliminationofi'anwanted metallic ions.--The unwanted metallic ions (in the caseWhere lime hasv been used as the neutralizing agent-calciumlmaylbeprecipitated in various ways, preferably by treating the filtrate with asubstance which will react with the unwanted metallic ionsin thesolution to form amaterial which can be precipitated safely.Investigations in this connection have demonstrated that improved yieldsof glutamic acid freefromunwanted impurities are obtained. when theresidual alkaline earth metal'ions areremoved as sulfite salts,providingthe reaction mixture during the formation and precipitation ofthe insoluble alkaline earth metal sulfite is maintained at a. pH ofabout 5.5 to 7.5. This is accomplished in the present:invention byreacting the alkaline hydrolysate (afterthe removal of the alkalineearth metal sulfate) with a soluble sulfite selected from the classconsisting of S02 and alkali metal and ammonium bisulfites and sulfites,the pHof the reaction'mixture beingmaintained at about 5.5-7.5 .byaddition of bases or acids where necessary. Where an acid material suchas' S02 (or its equivalent, sulfurovs acid) is employed, the. pH' of thereaction mix ture drop's'from the"v original 10.5-11.5 value andismaintained at the desired"5.5-7.5 value aesaiis by addition of smallamounts of caustic soda. Where alkali metal salts such as sodium orpotassium sulfite are employed, the pH may be lowered to the desired 5.5-7.5 Value by addition of acid such as l-lCl. The alkaline earth metalsulfite precipitate formed upon addition of the soluble sulfite isremoved by filtration or its equivalent. q

Concentration of glutamic acid Ziquor.ln the previous steps of theprocess, largely because of the necessity of using substantial amountsof wash water as an incident to the avoidance of loss in the filtrationsteps, the bulk has been increased to such an extent that the solutionmust be concentrated in order to facilitate proper crystallization ofthe glutamic acid. This is preferably effected in any desired type ofevaporating equipment, for example a vacuum pan, preferably at atemperature not exceeding 65 0., with a corresponding vacuum.Preferably, the concentrated solution should have a specific gravity offrom 1.20 to 1.25 at 40 C. During this concentration step, the pH hasbeen maintained at a point substantially above 3.2, the iso-electricpoint of l(+) glutamic acid, in order to prevent too earlycrystallization of the material.

The elimination of amino acids other than glutamic acid.The concentratedfiltrate from which the undesired metallic ions have been eliminatedaccording to the foregoing procedure, contains amino acids such astyrosine, leucine, and iso-leucine, and it is desirable to remove thesematerials before the pH is reduced to 3.2 for the crystallization ofl(+) glumatic acid. This removal is effected by maintaining the pH ofthe concentrated solution at a point substantially above that which isoptimum for the precipitation of glumatic acid, for example about 5.0 ormore, these unwanted amino acids being crystallized preferably byholding the solution at the desired pH for a suificient length of timeto permit crystallization to be substantially completed. A 24 hourholding period is usually sufficient, at room temperature. Thecrystallized amino are then removed by filtration or the equivalent. Thefiltrate containing the glumatic acid in solution is then conducted to acrystallizing vat or tank where the pH is adjusted to a point that isoptimum for the crystallization of glumatic acid, i. e. about 3.2, byaddition of hydrochloric acid or other suitable acidifying agent. Thecrystallization, when effected at room temperature, will require from 1to 6 days.

It will be understood that the cakes obtained from the first threefiltration steps will contain other unwanted substances in addition tothe substances mentioned as eliminated by said filtration steps. Forexample, in the first filtration step, a large amount of humin materialwill be taken out along with the calcium sulfate. However, in the finalcrystallization step, the crystals of l(+) glumatic acid will be foundto be of high purity and substantially uncontaminated with otherextraneous materials, so that, after the crystals have been separatedfrom the end liquor by a final filtration step or the equivalent, suchcrystals will be found to consist almost entirely of l(+) glumatic acid.The purity of the material is further shown by the fact that it is ofextreme whiteness and does not have the objectionable brown appearancewhich is shown by glumatic acid crystals initially produced by otherknown commercial processes. After washing, the crystals may be usedwithout further purification, in order to produce mono-sodium 4glutamate by mere treatment with caustic soda according to knownmethods.

The end liquor resulting from the foregoing process may, in certaininstances, be re-cycled once or twice, but eventually it is desirable toremove it from the system and convert it into a by-product which willcontain important quantities of various amino acids and some sodiumchloride resulting from the use of any sodium reagent in any prior stepof the process. This end liquor, in its original, concentrated or dryform, is a valuable flavoring material after its acidity has beenneutralized by known methods.

Example The procedure, so far as the hydrolysis step is concerned, iscarried on in the manner previously outlined. In the specific instance,a temperature of 115 C. is employed for a period of about 7 hours,gluten being the starting material and sulfuric acid being thehydrolytic agent.

After the hydrolysate is discharged from the hydrolyzer, a sufficientamount of water is added so that the slurry resulting from theneutralization step will be of the proper concentration for theparticular filtering equipment employed. The diluted hydrolysate is thencooled in the neutralizing tank, and, at that point, a sufiicient amountof hydrated lime, preferably in the form of a slurry of calciumhydroxide, is added to raise the pH to a point considerably in excess ofneutrality, for example, in the present instance, to about 11.0.

The result of this will be that the sulfuric acid will be substantiallyall converted to calcium sulfate, which being substantially insoluble,will be precipitated. The slurry resulting from the aforesaidneutralization step is then passed through a filtering or equivalentdevice, the temperature of the slurry at this point being about 70 C.The cake from the filtrate consists largely of calcium sulfate and huminmaterial.

It will be understood that, in order to avoid loss of valuable filtrate,it is advisable to follow up the hydrolysate with wash water. Thefiltrate, which, as has been stated, is still at a pH of 11.0, is thenconducted into a reaction tank where it is treated with S02. The S02reacts with the residual calcium ions in the filtrate to form calciumsulfite. During this step of the process, the pH which will be reducedby the addition of S02 should be maintained at a point close toneutrality, e. g. about pH 6. Otherwise undesirable efiects will appear.This may be effected by adding sodium hydroxide from time to time inthis stage of the process. However, it is found advantageous to add thispill-maintaining hydroxide along with the neutralizing line, since ithas no bad effect during any subsequent step of the complete process.This sodium hydroxide is added in the form of a strong aqueous solution,in an amount representing, in the form of solid sodium hydroxide, about10% of the weight of 02.0 added.

In such case, the amount of lime required to be added is correspondinglyreduced, and the amount of calcium ions in solution is very muchreduced, requiring much less S02 in the sulfite precipitation stage.

The slurry resulting from the last mentioned step of the process ispassed through a filter or similar equipment and is followed by washwater in the usual manner. The cake from this filter is substantiallyall calcium sulfite and residual unwanted color bodies. a

assent The filtrate is then treated with a -mineral acid, preferablyhydrochloric acid, so as to reduce the pH to between 5.5 to 6, and-theacidified filtrate is then conducted into a vacuum pan where, atatemperature of about 65 C. or less, it is concentrated to a specificgravity of about 1.22. The concentrated filtrate is then put into acrystallizer and held at room temperature for about 24 hours, duringwhich time the leucine, tyrosine and otheraminoacids, including about 8%methionine, will crystallize. This amino acid product, due to theefficiency of the combination of the. sulfate and sulfite precipitationsdescribed above, is light in color and practically free from inorganicmaterials. While it is any unwanted product as far as glutamic acid isconcerned, it serves asa good source for certain amino acids and istherefore a valuable by-product of the present invention.

To recover the glutamic acid,the slurry from the crystallizer isfiltered and washed. The filtrate is then handled in the same manner aspreviously described in connection with the general description.

In place of sulfur dioxide employed in the above example, the alkalimetal and ammonium bisulfites or sulfites may be employed if desired.The use of S02, however, is generally preferred as it does notcontaminate the reaction mixture with additional metallic ions. Asbetween the salts, the use of a bisulfite such as sodium bisulfite ispreferred over the sulfite salts for similar reasons, i. e. compared tosodium sulfite (NazSOa) only one half as much sodium (Na) per sulfite(S03) is added to the reaction mixture when sodium bisulfite (NaHSOs) isemployed. Also, as the hydrolysate at the start of the sulfite treatmenthas a pH of around 11 and the desired sulfite precipitation is carriedout at a pH around 5.5-7.5, and the subsequent processing steps arecarried out at an acid pH, the addition of acidic material which per selowers the pH of th hydrolysate as well as furnishes the precipitatingS03 ion, is for practical purposes generally preferred. The adjustmentof the pH by addition of acid, for example, before evaporation and theremoval of amino acids other than .glutamic acid, is not necessary whenthe sulfite treatment is carried out with acidic material at a pH around5.5 to 6.0.

lhe sulfite treatment of the present invention when carried out asdescribed above, purifies the amino acid containing reaction mixture bythe removal of unwanted materials including color bodies in addition tothe residual calcium as calcium sulfite. This additional purifyingaction results in the production of amino acids (including tyrosine,leucine, etc. as Well as glutamic acid) of improved color. Of particularimportance, the use of the sulfite treatment in accordance with thepresent invention also results in the recovery of increased yields ofglutamic acid.

The term soluble sulfite employed herein is directed to the classconsisting of sulfur dioxide, and alkali metal and ammonium sulfites andbisulfites, and chemical equivalents thereof. Included in the latter aresoluble sulfite or bisulfite salts formed in situ by reacting a basewith S02 e. g. SO2+NH3+I-I2O NH4OHL as well as sulfurous acid formed bydissolving S02 in water. All of these compositions are soluble in waterand provide the necessary ion for the removal of the residual alkalineearth metal as the sulfite precipitate.

The present invention is a continuation-in-part of my co-pendingapplication Serial No. 592,393,

filed May 7, 1945, now Patent 2,433,219 dated De cember 23, 1947.

I claim:

1. In the process of producing l(+) glutamic acid by hydrolysis of.protein with sulfuric acid in which the acidic hydrolysate is reactedwith a substantial excess of a compound selected from the classconsisting of alkaline earth metal oxides and hydroxides and theresultant alkaline earth metal sulfate precipitate is removed from thealkaline reaction mixture, the improvement which consists in reactingthe residual alkaline earth metal present in the alkalinereactionin-ixture with a soluble sulfite while maintaining the pH of themixture at about 5.5-7.5 and then removing the resultant alkaline earthmetal sulfiteprecipitate from the reaction mixture.

2. In the process of producing l(+) glutamic acid by hydrolysis of aprotein with sulfuric acid in which the acidic hydrolysate is reactedwith a substantial excess of a compound selected fromthe classconsisting of alkaline earth oxides and hydroxides and the resultantalkaline earth metal sulfate precipitate is removed from the alkalinereaction mixture, the improvement which consists in reacting theresidual alkaline earth metal present in the alkaline reaction mixturewith sulfur dioxide while maintaining the pH of the mixture at about5.5-7.5 and then removing the resultant alkaline earth metal sulfiteprecipitate from the reaction mixture.

3. In the process of producing l(+) glutamic acid by hydrolysis of aprotein with sulfuric acid inwhich the acidic hydrolysate is reactedwith a substantial excess of a compound selected from the classconsisting of alkaline earth metal oxides and hydroxides and theresultant alkaline earth metal sulfate precipitate is removed from thealkaline reaction mixture, the improvement which consists in reactingthe residual alkaline earth metal present in the alkaline reactionmixture with an alkali metal bisulfite while maintaining the pH of themixture at about 5.5-7.5 and then removing the resultant alkaline earthmetal sulfite precipitate from the reaction mixture.

4. The process of claim 3 in which the alkali metal bisulfite is sodiumbisulfite.

5. In the process of producing l(+), glutamic acid by hydrolysis of aprotein with sulfuric acid in which the acidic hydrolysate is reactedwith a substantial excess of a compound selected from the classconsisting of alkaline earth metal oxides and hydroxides and theresultant alkaline earth metal sulfate precipitate is removed from thealkaline reaction mixture, the improvement which consists in reactingthe residual alkaline earth metal present in the alkaline reactionmixture with an alkali metal sulfite while maintaining the pH of themixture at about 5.5-7.5 and then removing the resultant alkaline earthmetal sulfite precipitate from the reaction mixture.

6. The process of claim 5, in which the alkali metal sulfite is sodiumsulfite.

7. In the process of producing 1(+) glutamic acid by hydrolysis of aprotein with sulfuric acid in which the acidic hydrolysate is reactedwith a substantial excess of a compound selected from the classconsisting of alkaline earth metal oxides and hydroxides and theresultant alkaline earth metal sulfate precipitate is removed from thealkaline reaction mixture, the improvement which consists in reactingthe residual alkaline earth metal present in the alkaline reactionmixture with an ammonium sulfite while maintain,-

7 ing the pH of the mixture at about 5.5-7.5 and then removing theresultant alkaline earth metal sulfite precipitate from the reactionmixture.

8. In the process of producing l(+), glutamic acid by hydrolysis of aprotein with sulfuric acid, the improvement which comprises adding anexcess of calcium hydroxide to the acidic hydrolysate to obtain a pH ofbetween about 10.5 and 11.5 in the resulting solution, removing theresultant calcium sulfate precipitate from the reaction mixture,reacting the residual calcium present in the reaction mixture with S02while maintaining the pH of the mixture at about 5.5-7.5 and thenremoving the resultant calcium sulfite precipitate from the reactionmixture.

, 9. In the process of producing l(+) glutamic acid by hydrolysis of aprotein with sulfuric acid, the improvement which comprises adding an excess of calcium hydroxide together with sodium hydroxide to the acidichydrolysate to obtain a pH of between about 10.5 and 11.5 in theresulting solution, removing the resultant calcium sulfate precipitatefrom the reaction mixture, reacting the residual calcium present in thereaction mixture with S02 while maintaining the pH of the mixture atabout 6 and then removing the resultant calcium sulfite precipitate fromthe reaction mixture.

10. In the process of producing l(+) glutamic acid by hydrolysis ofgluten with sulfuric acid, the improvement which comprises adding anexcess of calcium hydroxide together with sodium hydroxide to the acidichydrolysate to obtain a pH of about 11 in the resulting solution,removing the resultant calcium sulfate precipitate from the reactionmixture, reacting the residual cal cium present in the reaction mixturewith $02 while maintaining the pH of the mixture at about 6 and thenremoving the resultant calcium sulfite precipitate from the reactionmixture.

FOREST A. HOGLAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

OTHER REFERENCES Mellor, Inorganic and Theoretical Chemistry, vol. 10,page 282 (1930), pub. Longmans, Green 8: Co.

Certificate of Correction Patent No. 2,533,114 December 5, 1950 FORESTA. HOGLAN It is hereby certified that error appears in the printedspecification of the above numbered patent requiring correction asfollows:

Column 3, line 45, after the word amino insert acids; column 6, line 23,after the Word earth insert metal;

and that the said Letters Patent should be read as corrected above, sothat the same may conform to the record of the case in the PatentOffice.

Signed and sealed this 13th day of February, A. D. 1951.

[SEAL] THOMAS F. MURPHY,

Assistant Commissioner of Patents.

1. IN THE PROCESS OF PRODUCING 1($) GLUTAMIC ACID BY HYDROLYSIS OF APROTEIN WITH SULFURIC ACID IN WHICH THE ACIDIC HYDROLYSATE IS REACTEDWITH A SUBSTANTIAL EXESS OF A COMPOUND SELECTED FROM THE CLASSCONSISTING OF ALKALINE EARTH METAL OXIDES AND HYDROXIDES AND THERESULTANT ALKALINE EARTH METAL SULFATE PRECIPITATE IS REMOVED FROM THEALKALINE REACTION MIXTURE, THE IMPROVEMENT WHICH CONSISTS IN REACTINGTHE RESIDUAL ALKALINE EARTH METAL PRESENT IN THE ALKALINE REACTIONMIXTURE WITH A SOLUBLE SULFITE WHILE MAINTAINING THE PH OF THE MIXTUREAT ABOUT 5.5-7.5 AND THEN REMOVING THE RESULTANT ALKALINE EARTH METALSULFITE PRECIPITATE FROM THE REACTION MIXTURE.